Method of impregnating a carbon electrode with a drying oil



April 7, 1959 C. C. HARDMAN METHOD OF IMPREGNATING A CARBON ELECTRODE WITH A DRYING OIL EXCESS OIL MIXTURE RETURNED TO STORAGE Filed June 21. 1955 IMPREGNATION TANK PREFERABLY APPLY VACUUM AND PRESSURE ALTERNATELY DRAIN EXCESS OF- MIXTURE FROM ELECTRODE HEAT EL ECTRODE POROUS CARBON ELECTRODE IMPREGNATED ELECTRODE INVENTOR CARL c. HARDMAN ATTORNEY METHOD OF IMPREGNATING A CARBON ELECTRODE WITH A DRYING OIL Carl C. Hardman, Parma Heights, Ohio, assignor to Diamond Alkali Company, Cleveland, Ohio, a corporation of Delaware Application June 21, 1955, Serial No. 517,087

5 Claims. (Cl. 117-228) This invention relates to improvements in electrolytic cells, and more particularly is concerned with the treatment of polymerizable oil-containing carbon electrodes for use in chlorine-alkali type electrolytic cells.

Various methods have heretofore been proposed to increase the durability and useful life of carbon electrodes in electrolytic cells. Typical of such a prior suggestion is the impregnation of a carbon electrode with a drying oil, which oil then is allowed to dry or harden in situ.

the partially-cured oil and, in the case of a chlorine-alkali cell employing such an electrode as an anode, a subsequent chlorination of the oil. While this chlorination not only reduces the chlorine output of the cell and introduces undesired by-products, an additional problem is involved, since the finely-divided chlorinated oil is deposited over the cell diaphragm, thus rapidly reducing the fluid flow therethrough and generally completely plugging the diaphragm in a short time. herent problem in such chlorination is the formation of by-product HCl in the anolyte, which HCl, of course, undesirably reduces the pH of the anolyte.

Prior workers in the art have sought a method to overcome these difficulties and various treatments have been proposed to eliminate or minimize these problems. Illustrative of prior suggestions and practice to improve the operating characteristics of impregnated carbon electrodes is the storage of freshly-impregnated anodes for a considerable period of time to allow gradual hardening and solidification of the oil within the anode pores, or the use of a special conditioning electrolytic cell in which the unpolymerized oil is leached from the electrode prior to use in a commercial cell. However, so far as is know-11,.

up to the present time no completely satisfactory solution to the problem had been discovered.

It is, therefore, a principal object of this invention to avoid the difliculties heretofore encountered in the operation of electrolytic cells and to provide a new and improved electrode treatment.

A further object of this invention is the provision of new and improved carbon electrodes for use in electrolytic cells.

A still further object of the invention is to provide new and improved carbon electrodes impregnated with a polymerizable oil, which electrodes do not interfere with the normal operation of an electrolytic cell.

In accordance with the present invention, a carbon electrode is contacted with a polymerizable oil and thereafter treated toetfect polymerization atuagreatlyaccela J v erated rate, in a novel manner. More particularly, the

A further in- 'pleted within a relatively short time.

2,881,100 Patented Apr. 7, 1959 ice nate a carbon electrode with a polymerizable oil, with or without such prior treatment as a pitch-impregnation and/ or graphitizing, and in a very short time to convert the polymerizable oil to a substantially completely polymerized substance Within the carbon pores, thereby to preclude leaching of the oil from the anode upon initial use in a chlorine-alkali electrolytic cell.

Up to this time it has been known to use driers such as various cobalt compounds to accelerate the curing of various oils, especially in paints. However, the present invention is based upon the discovery that by combining two distinctly different types of driers, a novel and synergistic result is obtained. More particularly, it has been found that by combining a so-called through drier with a so-called surface drier, the polymerization of oil within a carbon electrode can be substantially com- This, of course, is in marked contrast tothe extended periods of time heretofore required for anything approaching a complete polymerization of oil contained in carbon electrodes.

Theexpression through drier, as used throughout the specification and claims, is intended to mean a substance which promotes substantially uniform hardening of a polymerizable oil throughout the oil thickness. Illustrative of such compounds are lead compounds, e.g., the presently preferred being lead naphthenate. larly, the expression surface drier is intended to mean a substance which produces a pronounced drying effect at the surface of a polymerizable material containing such a drier. Illustrative of such driers are various copper and cobalt compounds, ,for example, cobalt naphthenate which is now preferred.

In the practice of this invention, use is made of a synergistic mixture of a surface drier and a through dryer in order to obtain a substantially complete polymerization of oil Within a carbon electrode without the difficulties heretofore encountered. At present, it is preferred to employ a mixture of a cobalt compound and a lead,

compound as the respective surface drier and through drier.

It is also now preferred to employ a major proportion of a surface drier and a minor proportion of a through drier. Superior results are obtained when these proportions are approximately 10:1 by weight, that is, 10 parts by weight of a surface drier, e.g., a cobalt compound to 1 part by weight of a through drier, e.g., a lead compound. Illustrative of a preferred embodiment of the invention is a mixture of 10 parts by weight of cobalt naphthenate with 1 part by weight of lead naphthenate. Such a synergistic mixture can be employed in lieu of, or in admixture with, prior catalysts used with polymerizable oil compositions.

It is also a feature of this invention to employ in the impregnation of carbon electrodes a polymerizable oil, preferably linseed oil, which has been treated or modified with fumaric acid to improve its polymerization properties 'and/ or to render it more highly viscous.

In order that those skilled in the art may more completely understand this invention and its practice, the following specific examples are ofiered.

EXAMPLE I q Simiten parts of raw linseedoil and one part of a mixture of cobalt naphthenate and lead naphthenate in a proportion of parts by weight cobalt naphthenate to 1 part by weight lead naphthenate. The thus-treated anode is then heated to effect substantially complete polymerization. The resultant anode is adapted for use in a chlorinealkali electrode cell wherein it exhibits excellent properties.

In the practice of this invention it has been found that excellent results are obtained when a carbon electrode, typically a carbon anode as used in a chlor-alkali diaphragm cell, is impregnated with a polymerizable oil, such as the presently preferred linseed oil, tung oil, perilla oil, fish oil, saffiower oil, soybean oil, oiticica oil, or dehydrated castor oil.

Other oils which in many applications may be employed in lieu of, or in admixture with, the foregoing oils, either wholly or in part, are coconut oil, palm kernel oil, babassu oil, murumuru oil, palm oil, rape seed oil, mustard seed oil, olive oil, peanut oil, sesame oil, corn oil, cottonseed oil, soybean oil, sunflower oil, walnut oil, whale oil, menhaden oil, sardine oil, and herring oil.

One qualitative test known to the art as indicative of the condition of a drying oil in the electrode and useful in the practice of this invention is the so-called smoke test. This test involves heating an oil-impregnated electrode to a temperature at which the oil smokes. If no oil exudes from the electrode at this temperature, it is generally considered that the electrode is suitable for use in an electrolytic cell.

While details vary somewhat in commercial production of carbon anodes, generally, finely-divided coke is mixed with the desired proportions of a binder, usually a coal tar residue pitch. This mixing generally is carried out at an elevated temperature sufiicient to melt the binder. The resultant mixture is then extruded and the thusformed structure baked, typically at a temperature of' about 1800 F to remove volatile matter. Anodes produced in the foregoing manner may then advantageously be impregnated with a drying oil in accordance with this invention.

Superior results are obtained in most instances, however, when, prior to impregnation with a drying oil, the anode is graphitized, i.e., the carbon crystal structure is converted to the graphitic crystal structure by heating one or more times to a temperature in the range from 41S0-5000 F. At times, either a baked anode or graphitized anode can be further treated with pitch when it is desired further to improve the anode density and strength. Impregnation of the carbon anode with a drying oil can be accomplished in any conventional way, as by placing the anodes under vacuum and immersing the anodes while under vacuum into the desired impregnant. Illustrative of one specific method for impregnating a carbon anode is the following:

EXAMPLE H A graphitized carbon anode is placed into an autoclave and a 28" Hg vacuum applied for minutes to remove air from the anode pores. Linseed oil, heated to a temperature of 250 F., is then drawn into the autoclave and a pressure of 90 p.s.i.g. is applied for one hour. The excess linseed oil is then forced back into its heating tank and the anode surface is contacted eight times with superheated steam (300 F.) to remove surface retained oil.

EXAMPLE III A carbon electrode is impregnated with a mixture of 220 cc. linseed oil (200 gms.), 3.3 gms. cobalt naphthenate, 10 gms. fumaric acid dissolved in 90 cc. dimethyl formamide, and 120cc. acetone. The thus-impregnated electrode is then heated for 24 hours at 300 F. in a nonoxidative atmosphere to complete its preparation for use in a chlorine-alkalielectrolytic cell.

4 EXAMPLE IV Part A A carbon electrode is impregnated with the following safflower oil composition:

Safiiower oil "cc..- 280 Acetone cc-.. Lead naphthenate g s 7.8 Cobalt naphthenate "gms-- 3.1

by application of pressure to force this composition into the electrode while maintained in a vacuum. The thustreated electrode is then exposed to steam for one hour and subsequently is heated to a temperature of 300 F. for 24 hours.

Part B Time (111111.) DH

Thus, it will be appreciated that an electrode of the present invention is quite stable and that little, if any, oil is leached therefrom.

EXAMPLE V The procedure of Example IV is repeated using as a carbon impregnant the following composition:

Raw linseed oil cc 280 Acetone cc 120 Lead naphthenate gms 7.8 Cobalt naphthenate gms 3.1

Equally advantageous results are obtained.

It is to be understood that although the invention has been described with specific reference to particular embodiments thereof, it is not to be so limited, since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

What is claimed is:

1. In the method of treating a porous carbon electrode including the steps of impregnating said electrode with a drying oil and heating the thus-impregnated electrode to elTect polymerization of said drying oil, the improvement which comprises combining said drying oil with a mixture of lead and cobalt naphthenates, said mixture containing approximately from 289l% of cobalt naphthenate and from 9% to 72% of lead naphthenate, the amount of said mixture being from approximately 4% to 10% of the weight of said drying oil.

2. The method of claim 1 wherein the amount of said mixture is 10% of the weight of said drying oil and the proportion of said lead naphthenate to said cobalt naphthenate is 10:1.

3. The method of claim 2 wherein said drying oil is mixture is approximately 4% of said drying oil and the proportionof cobalt. naphthenate is 2.5: 1..

5. The method of claim 4 wherein said drying oil is linseed oil.

References Cited in the file of this patent UNITED STATES PATENTS 6 Kiefer et a1. Jan. 30, 1945 Lecture et a1. Feb. 27, 1951 Rust e! a]. Aug. 14, 1951 Brophy Mar. 2, 1954 Grummitt May 18, 1954 McLaughlin et a1. Apr. 30, 1957 

1. IN THE METHOD OF TREATING A POROUS CARBON ELECTRODE INCLUDING THE STEPS OF IMPREGNATING SAID ELECTRODE WITH A DRYING OIL AND HEATING THE THUS-IMPREGNATED ELECTRODE TO EFFECT POLYMERIZATION OF SAID DRYING OIL, THE IMPROVEMENT WHICH COMPRISES COMBINING SAID DRYING OIL WITH A MIXTURE OF LEAD AND COBALT NAPHTHENATES, SAID MIXTURE CONTAINING APPROXIMATELY FROM 28-91% OF COBALT NAPHTHENATE AND FROM9% TO 72% OF LEAD NAPHTHENATE, THE AMOUNT OF SAID MIXTURE BEING FROM APPROXIMATELY 47 TO 10% OF THE WEIGHT OF SAID DRYING OIL. 